Yes
When first written, The Silmarillion did not contain any Ents, because it was written prior to the point where Tolkien invented them. Tolkien did his last set of major revisions to the Silmarillion in 1951, shortly after finishing the writing of The Lord of the Rings, but did not take the opportunity to add in Ents.
He seems to have not seriously considered it until September 1963, when answering a letter to a reader. Tolkien acknowledged the absence of Ents in the first age stories as then written, and expressed a need to correct this.
There are or were no Ents in the older stories – because the Ents in fact only presented themselves to my sight, without premeditation or any previous conscious knowledge, when I came to Chapter IV of Book Three. But since Treebeard shows knowledge of the drowned land of Beleriand (west of the Mountains of Lune) in which the main action of the war against Morgoth took place, they will have to come in. But as the War in Beleriand was at the time of the hobbits’ meeting some 7,000 years ago, no doubt they were not quite the same: less wise, less strong, shyer and more uncommunicable (their own language simpler, but their knowledge of other tongues very small).
September 1963 Letter to Colonel Worskett (Letters of J.R.R. Tolkien #247)
Tolkien then went on two list two possible ways they could play a part in first age:
1. The Ruin of Doriath
But I can foresee one action that they took, not without a bearing on The L.R. It was in Ossiriand, ... that Beren and Lúthien dwelt for a while after Beren’s return from the Dead (I p. 206). Beren did not show himself among mortals again, except once. He intercepted a dwarf-army that had descended from the mountains, sacked the realm of Doriath and slain King Thingol, Lúthien’s father, carrying off a great booty, including Thingol’s necklace upon which hung the Silmaril. There was a battle about a ford across one of the Seven Rivers of Ossir, and the Silmaril was recovered ... It seems clear that Beren, who had no army, received the aid of the Ents – and that would not make for love between Ents and Dwarves.
September 1963 Letter to Colonel Worskett (Letters of J.R.R. Tolkien #247)
As Tolkien last wrote this chapter in 1930, there were no Ents, just Beren and the Green Elves of Ossiriand.
This ford the Dwarves must pass ere they reached their homes; and there Beren fought his last fight, warned of their approach by Melian. In that battle the Green Elves took the Dwarves unawares as they were in the midst of their passage, laden with their plunder; and the Dwarvish chiefs were slain, and
well nigh all their host.
The Quenta Nolorwina section 14 (The Shaping of Middle-earth)
In the 1950s, Tolkien was unhappy with this account, and while he didn't revise the chapter, when mentioning the event in some other texts he began attributing this role to at first Curufin and Celegorm and then to Caranthir. (See The War of the Jewels - "The Tale of Years")
Christopher Tolkien ultimately decided that the chapter as it existed from 1930 was unusable and to rewrite most of it from scratch. While doing so, he decided to follow the later 1963 letter, bringing the role back to Beren and introducing the Ents himself.
And as they climbed the long slopes beneath Mount Dolmed there came forth the Shepherds of the Trees, and they drove the Dwarves into the shadowy woods of Ered Lindon: whence, it is said, came never one to climb the high passes that led to their homes.
The Silmarillion - Of the Ruin of Doriath
The ambush and destruction of the Dwarves at Sarn Athrad was given again to Beren and the Green Elves (following my father's letter of 1963 quoted on p. 353, where however he said that 'Beren had no army'), and from the same source
the Ents, 'Shepherds of the Trees', were introduced.
The War of the Jewels - "A note on Chapter 22 Of the Ruin of Doriath
in the published Silmarillion"
2. The origin of Ents
No one knew whence they (Ents) came or first appeared. The High Elves said that the Valar did not mention them in the ‘Music’. But some (Galadriel) were [of the] opinion that when Yavanna discovered the mercy of Eru to Aulë in the matter of the Dwarves, she besought Eru (through Manwë) asking him to give life to things made of living things not stone, and that the Ents were either souls sent to inhabit trees, or else that slowly took the likeness of trees owing to their inborn love of trees. (Not all were good [words illegible]) The Ents thus had mastery over stone. The males were devoted to Oromë, but the Wives to Yavanna.
September 1963 Letter to Colonel Worskett (Letters of J.R.R. Tolkien #247)
Following this letter, Tolkien wrote a short work titled "Of the Ents and Eagles" or "Anaxartaron Onyalië", describing the origin of Ents. This text was incorporated by Christopher into the second chapter of the published Silmarillion, and artificial chapter that Christopher constructed by moving the account of the creation of the Dwarves to the beginning of the book.
In conclusion:
- Ents were not invented by Tolkien until after the Silmarillion was first written
- Tolkien never added any mention of them into the Silmarillion himself
- In 1963, in response to a letter, Tolkien decided that he would add them in, and proposed two ways in which to do so
- Both of the ways that Tolkien proposed were acted on by Christopher when editing the book for publication, and you have already noted them in your question
